About Fluid Exchange

Fluid exchange describes the flow of fluid between two fluid cavities or between a fluid cavity and its environment.

Fluid exchange allows you to model flow activities, such as the venting of a cavity through an exhaust orifice, the transfer of fluid through cavity walls, or the leakage of fluid through a porous fabric.

This page discusses:

See Also
Defining the Fluid Flow In and Out of Fluid Cavities

Fluid Exchange Methods

You can describe how the fluid flows into or out of a fluid cavity by using one of the following methods:

Method Description
Bulk viscosity The fluid exchange rate is based on the viscous resistance coefficient and the hydrodynamic resistance coefficient.
Mass flux The fluid exchange rate is based on the mass flow rate per unit area for the effective area.
Volume flux The fluid exchange rate is based on the volumetric flow rate per unit area for the effective area.
Energy flux The fluid exchange rate is based on the energy flux per unit area for the effective area.
Mass rate leakage The fluid exchange rate is based on the mass rate of flow out of one fluid cavity as a function of the pressure difference between the fluid cavities or between the leaking fluid cavity and the environment.
Volume rate leakage The fluid exchange rate is based on the volumetric rate of volume flow out of one fluid cavity as a function of the pressure difference between the fluid cavities or between the leaking fluid cavity and the environment.
Energy rate leakage The fluid exchange rate is based on the energy rate of volume flow out of one fluid cavity as a function of the pressure difference between the fluid cavities or between the leaking fluid cavity and the environment.
Fabric leakage The fluid exchange rate is based on the mass flow rate of fluid through the fabric between the fluid cavities or between the leaking fluid cavity and the environment.
Orifice The fluid exchange rate is based on the mass flow rate of fluid through a vent or exhaust orifice.
User The fluid exchange rate is based on user subroutines VUFLUIDEXCH and VUFLUIDEXCHEFFAREA.

Effective Leakage Area and Heat Exchange

For fluid exchange occurring during an explicit dynamic step, the flow rate into or out of a fluid cavity is proportional to the effective leakage area, which is the area representing the interface between the fluid cavity and the environment or between the two fluid cavities. The leakage area might represent the size of an exhaust orifice, the area of a porous fabric enclosing the cavity, or the size of a pipe between cavities. You can specify the effective leakage area directly as part of the fluid exchange definition.

The app includes heat energy in the fluid exchange analysis in explicit dynamic steps, and the app calculates the heat exchange based on the temperature difference between the two cavities or between the cavity and its environment. You cannot specify heat exchange directly in terms of a constant heat flux.